14 Lectures on Bacteria. [^ ii. 



ducing on substances rich in starch, such as dressed potatoes, 

 bread, rice, or wafers, moist blood-red spots which sometimes 

 spread rapidly and widely. Their colour has given rise to a 

 variety of superstitious notions when they have appeared 

 unexpectedly on objects of household use. They consist of 

 one of the chromogenous Bacteria which have been already 

 mentioned. 



It was stated above that the grouping of different forms is 

 different in the same fluid, and in like manner the conformation 

 of the Zoogloeae on solid substances shows manifold variation 

 of forms which differ in other respects also. 



These various facts connected with the grouping are them- 

 selves calculated to afford very valuable marks for character- 

 ising and distinguishing forms, the more valuable indeed in 

 proportion to the difficulty oftentimes of discriminating in- 

 dividual cells of such minute size under the microscope. It is 

 precisely in the phenomena of grouping that specific peculiarities 

 of conformation best display themselves, being collected together, 

 as it were, in larger quantity; these characters must indeed 

 be present in the single cell, but, with the means at present 

 at our disposal, it is difficult or even impossible to recognise 

 them there. But there is nothing peculiar in this. There 

 are many cells of gigantic size in comparison with the Bacteria 

 and highly differentiated, of which we cannot say with cer- 

 tainty when we see them by themselves whether they belong 

 to a lily or a tulip. But in their natural connection or grouping 

 some of them form a lily, others a tulip, and by this we know 

 that they are different. 



